1. Field of the Invention
The present invention relates generally to disk drives, and particularly to a gimbal-level piezoelectric microactuator for read/write heads for disk drives.
2. Description of Related Art
One of the main avenues for the increase in storage capacity of disk drives is through reduction of the track pitch of the recorded information. The minimum distance between recorded data tracks is limited by the ability of a voice coil motor (VCM)-actuated servo system to accurately maintain the position of the recording heads over a given track.
The positioning capability of this servo system is limited by its bandwidth, which in turn is constrained by the power available to the VCM and by suspension resonances. The resolution of the actuator's motion is also limited by stiction in the pivot's ball-bearings. Both of these constraints are approaching fundamental limits after which further increase in track density will be not be possible with the current technology.
To improve track density, proposals have been made to implement a second-stage, for fine-positioning, in addition to the first-stage, for coarse positioning. For example, Takaishi et al. propose a secondary microactuator which is built into the head assembly structure, as part of the head mounting block, between the head suspension and the head assembly arm ("Microactuator Control For Disk Drive", Takaishi et al., IEEE Transactions on Magnetics, Vol. 32, No. 3, May 1996). Another secondary actuator arrangement is described in U.S. Pat. No. 5,521,778 to Boutaghou et al., wherein the secondary actuator 30 connects one end of a further arm portion (a load beam 25) to an actuator arm 24 and wherein a slider 26 and head are supported at the opposite end of the load beam 25.
In each of the above-referenced proposed systems, a substantial length of the head support structure is located between the head and the secondary actuator. For example, as shown in FIG. 4 of the Takaishi et al. article, a head suspension, which accounts for a significant portion of the length of the structure supporting the head, extends from the secondary actuator to the head. Similarly, as shown in FIG. 1 of the Boutaghou et al. patent, the load beam 25, which accounts for about one-half of the length of the structure supporting the head, extends from the secondary actuator to the head.
As such, each of these structures may be susceptible to a significant level of structural resonance, upon operation of the secondary actuator. Such resonance tends to result in unwanted head motion, which inherently reduces the accuracy of the positioning operation and, thus, reduces the available track density.
In the related provisional application Ser. No. 60/051,694 referred to above there is disclosed a suspension-level piezoelectric microactuator, which structurally is relatively small and not necessarily compatible with existing disk drive structures. Further, there is a need to improve the flexure of the microactuator and to obtain improved sensitivities, and, consequently, accuracies.
Accordingly, there is a need in the art for a microactuator for supporting and finely-positioning a read and/or write head with sufficient accuracy to operate with a track pitch substantially below that possible with typical VCM servo system operation.